1. Field of the Invention
This invention relates generally to a high frequency oscillatory ventilation apparatus for artificial respiration and particularly to an oscillator for use in such ventilation apparatus.
2. Related Art
Japanese Utility Model Application No. 59-17747 discloses a high frequency oscillatory ventilation apparatus for artificial respiration shown in FIG. 1. This ventilation apparatus comprises a pneumatic circuit including a patient circuit 10 including an inspiration tube 12a and three tubes 12b, 12c and 12d, these four tubes being connected together at a junction point to communicate with one another. An oscillator 14 comprises a cylinder unit including a cylinder 14a and a piston 14b received in the cylinder 14a, and a motor 16 connected to the piston 14b through a crank 18 and a connecting rod 20, so that the piston 14b is reciprocably moved along the cylinder 14a. The tube 12b is connected to the oscillator 14, so that the oscillator 14 imparts oscillation normally at a high frequency of not less than 4 Hz to respiratory gas in the patient circuit 10, thereby promoting the diffusion of the gas in the respiratory tract of the patient to effect artificial respiration. The tube 12d is connected to a moistening/gas feed tube 22 to feed respiratory gas from a gas source 24 to the patient circuit 10, and a respiratory pressure-detecting line 26 is connected to the tube 12b. A positive-pressure generating unit 28 comprises a cylindrical member 28, a and a nozzle 28b having a discharge end received loosely in an open end of the cylindrical member 28a. The respiratory gas is fed from the gas source 24 to a gas feed conduit 30 via any one of the following three feed paths:
(1) the first path constituted by a conduit 31 connected to the outlet side of a solenoid valve 32, a regulator 33 and a check valve 34.
(2) the second path constituted by the conduit 31, a regulator 35, a check valve 36 and a solenoid valve 37.
(3) the third path constituted by the conduit 31 and the solenoid valve 37. The solenoid valve 32 is controlled by a controller 38 including a microprocessor to selectively feed the respiratory gas from the gas source 24 to the conduit 31. The solenoid valve 37 has two inlets 37a and 37b and one outlet 37c, and under the control of the controller 38, the solenoid 37 has three modes of operation. More specifically, in a first mode, the first inlet 37a communicates with the outlet 37c, and in a second mode, the inlet 37b communicates with the outlet 37c, and in a third mode, the solenoid 37 is closed. Pressure gauges 39 and 40 monitor the output pressures of the regulators 33 and 35, respectively. The output pressures of the regulators 33 and 35 are set at different predetermined levels, respectively. With this arrangement, the pressure of the respiratory gas fed to the nozzle 28b can be changed by selecting any one of the above three feed paths, so that the pressure in the cylindrical member 14a is always kept at pressure P1 lower than the pressure P2 of the respiratory gas in the patient circuit 10.
A branch conduit 41 is connected between the oscillator 14 and the patient circuit 10. A plug 42 is mounted on the open end of the branch conduit 41 through which it communicates with the atmosphere, and the plug 42 is actuated by a solenoid 43 to selectively open and close the open end of the branch conduit 41. The solenoid 43 is operated under the control of the controller 38 in accordance with a detected value of a pressure sensor 44, so that the pressure P2 in the patient circuit 10 is always kept higher than the pressure P1 in the positive pressure-generating unit 28. With this arrangement, the breathing gas and the respiration gas from the gas source 24 can be smoothly discharged from the ventilation apparatus via the positive pressure-generating unit 28.
A protective circuit 45 is connected between the solenoid valve 32 and the pressure sensor 44 for preventing moisture from intruding from the patient circuit 10 into the pressure sensor 44 through the pressure detecting line 26. The protective circuit 45 comprises a gas regulator 46, a pressure switch 47, a resistor 48. When the respiratory gas does not flow properly from the regulator 46 to the pressure sensor 44, the pressure switch 47 is activated to feed an alarm signal to the controller 38.
Those portions of the above ventilation through which the expired gas from the patient pass, such as the patient circuit 10, the conduits adjacent thereto and the interior of the cylinder unit of the oscillator 14, must be cleaned and sterilized for the next use. Heretofore, the patient circuit and the conduits adjacent thereto, once used, have been discarded since they are relatively inexpensive. However, the cylinder unit could not be disposed of once it is used because it is relatively expensive. Therefore, each time the cylinder unit is used, it is cleaned and sterilized. The cylinder unit of the oscillator 14 is coupled to the motor 16 and also fixed to a base plate, though removably. Therefore, each time the cleaning and sterilization are effected, the coupling between the cylinder unit and the motor must be released, and the cylinder unit must be removed from the base plate. In addition, the motor must be detached from the base plate. Thus, the maintenance of the ventilation apparatus is rather cumbersome.